PURPOSE: To provide a low NOx state and assure a stable combustion by a method wherein a first stage fuel nozzle is constructed under a combination of a dispersion combustion nozzle and a pre-mixed combustion nozzle and a diameter of the pre-mixed combustion part is formed to be shorter than that of its downstream side.

CONSTITUTION: A gas turbine combustion device 15 is operated such that fuel is injected by a first stage fuel supplying means 30 into a first stage combustion region 26 within a combustion device liner 20 and in turn fuel is injected into a second stage combustion region 27 by a second stage fuel supplying means 32 under a lean state of fuel and the fuels are ignited within the combustion device liner 20. The first stage fuel supplying means 30 is constructed under a combination of a dispersion combustion nozzle 35 and a pre-mixed combustion nozzle 36, wherein a dispersion combustion having a superior combustion efficiency and stable combustion is realized by the dispersion combustion nozzle 35 and at the same time at the pre-mixed combustion nozzle 36, the diameter of the pre-mixed part at its upstream side is shorter than that of its downstream side so as to perform a stable combustion of the pre-mixed gas and to prevent its back-fire. Accordingly, a stable combustion can be attained and a low NOx state may also be provided even under a state in which a rate of dispersion combustion with a frequent occurrence of NOx is quite low.